1. Field of the Invention
The present invention relates to a screw driver, and more particularly to a ratchet screw driver.
2. Description of the Prior Art
The applicant has developed three typical screw drivers which are disclosed in U.S. Pat. No. 5,782,146 to Lin, U.S. Pat. No. 5,875,692 to Lin, and U.S. Pat. No. 5,967,003 to Lin. The ratchet mechanisms of the typical screw drivers include one or more pairs of ratchet gears rotatably and/or slidably engaged on a driving stem and received in the handle. The typical screw drivers have no devices that may be used to operate or move the ratchet gears relative to each other.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages of the conventional screw drivers.